Now, you could edit the .PK3 file to add an edited br_warehouse_mini.cfg, but you'd download a the original .PK3 as an additionaly copy the next time you connect to a server if it is played.

You can always load the map via \map br_warehouse_mini in console, without changing anything (which is what I recommend). Last but not least, I intentionally didn't deliver a cfg file for br_nonamecityold, because I didn't want to confuse people.